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pol·y·gon
/ˈpäliˌgän/
Noun

A plane figure with at least three straight sides and angles, and typically five or more.

tri·an·gle
/ˈtrīˌaNGgəl/
Noun

A plane figure with three straight sides and three angles.
A thing shaped like such a figure.

Can be identical but they are not the same thing. Correct me if I'm wrong, but polygons are further divided into triangles in 3D design programs because it's simpler to think of polygons as a collection of consistent, easily definable entities rather than one very complex plane. You can be sure that the polycount on those models is not the same as the triangle count. Unless you're modelling a perfectly flat and pointy d4 then those numbers will never be identical (and even in that scenario the triangles may be subdivided into smaller ones, I'm not completely sure).